FLEAS 95 



In considering the evolution of a genus like these bird fleas which 

 appear to have been derived at least twice from closely related mammal 

 fleas — possibly at different times and in widely separated parts of the 

 world, it must not be forgotten that certain characters from an ancestral 

 flea may also re-appear in different branches of one stem. 



One very interesting Ceratophyllus must be mentioned here. Although 

 it has not yet turned up in Britain it seems to us there is quite a 

 good chance that it will eventually be discovered on the stoat and 

 marten in Northern Scotland. This is C. lunatus, a former bird flea 

 recorded from the Alps, Alaska, North Sweden and Northern Russia, 

 which has once again reverted to a life on mammal hosts. This return 

 to its original type of host must have happened before or during the last 

 Ice Age, judging from the famihar boreal-alpine distribution (see 

 p. 87) of the flea. It also must have occurred fairly early in its history 

 as a bird flea, for although it displays certain features typical of bird 

 CeratophyUi the modifications of thereceptaculum seminis usually assoc- 

 iated with an avian host have been arrested at a relatively early stage. 



The fact that there are several bird fleas with the boreal-alpine 

 type of distribution proves that they had already changed on to avian 

 hosts at any rate before the end of the last Ice Age in Europe. 



The Effect upon the Flea of a Change 

 TO A Bird Host 



It has been pointed out (p. 90) that the change over to bird from 

 mammal host must have taken place in relatively recent times. Never- 

 theless, this new environment which involves such great differences in 

 food, temperature and habitat, has already left its mark upon the fleas. 



A study of the Ceratophylhdae and the PuHcidae shows that the 

 trends of evolution are different within the two main famihes or super- 

 families. When a switch over to a bird host occurs it seems to speed up 

 these family trends. 



In the GeratophylHdae there are four genera of bird fleas, Cerato- 

 phyllus, OrneacuSj Dasypsyllus and Mioctenopsylla, and two species from 

 the genus Frontopsylla* (chough fleas) which have unquestionably been 

 evolved from different groups of mammal fleas (p. 91). Nevertheless, 



♦Since the completion of this manuscript Frontopsylla laetus has been found by 

 Allan (1950) in a house-martin's nest in Kincardineshire, Scotland. 



